Tumor cells are often found in the blood of patients with various early stages of cancer as “micrometastases” (disseminated tumor cells), and are also found in metastatic cancers. The number of tumor cells in blood depends on the stage and type of the tumor. Tumors are extremely heterogeneous. As a result, a biopsy from a single site might not represent the heterogeneity in a tumor population. Biopsies are typically obtained on primary tumors; however, most metastatic tumors are not biopsied, making molecular analysis of tumor samples even more difficult.
During tumor metastasis, the most aggressive tumor cells leave the primary tumor and travel through the blood and lymphatic system to reach a distant location. Thus, circulating tumor cells from blood represent the most aggressive and homogenous population of tumor cells. The number of metastatic tumor cells in blood can vary from one to several thousand cells per milliliter of blood. Accordingly, specific and sensitive methods are needed to detect these cells for diagnostic and prognostic purposes. The present invention satisfies this need and provides related advantages as well.